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Old 25th March 2012, 05:09 PM   #1
AC439 is offline AC439  United States
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Question Chassis vibration ! How to solve ?

As stated in my other post, I just finishing up my 1996 JLH amplifier and I'm really enjoying it. But I do have one last problem to solve - vibration chassis.

The chassis is a steel enclosure and the power transformer causes the top panel to vibrate at 60Hz. I'm thinking to put a stud connecting the bottom and the top panel to lower the vibration but it may not work because the bottom is steel as well and it may also vibrate. Wonder if an aluminum bracket across the top and have a couple of screws bolting the top panel with the bracket will help ?

Any ideas ?
Thanks.
AC
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Old 25th March 2012, 05:25 PM   #2
AndrewT is offline AndrewT  Scotland
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Stiffening braces to change the natural resonant frequency of the panel.
Damping pads to both change the resonant frequency and also lower the Q

Be careful with damping. They will increase the chassis internal temperature.
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Old 25th March 2012, 05:27 PM   #3
AC439 is offline AC439  United States
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Thanks Andrew....I will definitely look into these ideas !
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Old 25th March 2012, 06:20 PM   #4
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The Citation 12 amplifier mounted the power transformer with rubber grommets. A 1/2" hole was used, the grommet fit in the hole and then washers on each side clamped the grommet.
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Old 26th March 2012, 01:42 PM   #5
AC439 is offline AC439  United States
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Thanks Simon, but the vibration of the top panel comes from the magnetic coupling from the mains transformer. The transformer itself doesn't vibrate.
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Old 26th March 2012, 03:04 PM   #6
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The system moves the transformer far enough off the chassis the magnetic field coupling is reduced by enough you shouldn't notice the vibration. Capacitors with DC voltage across them can produce signal due to vibration!
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Old 26th March 2012, 04:52 PM   #7
AndrewT is offline AndrewT  Scotland
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Quote:
Originally Posted by AC439 View Post
The transformer itself doesn't vibrate.
I will guarantee it does.

The vibration of the transformer sitting on your hand could be well damped and it is inaudible.
Place the transformer on a sponge and again it could be inaudible.
Place the transformer on a resonant panel and the combination of transformer + panel could be very audible.

How did the needle and transducer of the horn (non powered) record players work?
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Old 26th March 2012, 08:26 PM   #8
AC439 is offline AC439  United States
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Andrew, you are right. I think I didn't make it clear enough. Of course, I do feel the vibration of the transformer, but the vibration of the top panel is a lot more compare to the transformer (they are not touching each other). Too bad the only way to mount the transformer (it is relatively big) is to mount it sideways. The tranny is flushed with the top and the bottom panels. When I turn on the amp. The initial magnetic flux from the tranny couples mostly to the top panel such that it will even pull the panel towards the transformer and making a metallic impact sound !

I am going to post pics on Wed (when I'm off work).

Thanks !
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Old 28th March 2012, 09:15 PM   #9
AC439 is offline AC439  United States
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Smile Pics here...

Here's a pic of the location of the transformer. It is so big that it basically fits snug inside the chassis top to bottom. Definitely a toriodal transformer will solve the problem but I'm not ready to spend another $50~60 for a new transformer yet. I think I may try some dampening first and see how it goes......

-AC
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